1. Field of the Invention
The present invention relates to a method of forming a copper wire on a semiconductor device, and more particularly to a method of forming a copper wire on a semiconductor device that prevents the natural oxidation of copper.
2. Description of the Prior Art
Lately, semiconductor devices are becoming more integrated and their processing technologies are correspondingly being improved. Therefore, a process using copper (Cu), instead of aluminum (Al) as in the prior art, for making a wire has been proposed as an effort to make speed, resistance or parasitic capacitance between metals of the devices. Moreover, instead of an insulation film made of an oxide as used in the prior art, an insulation film made of a material with a low dielectric constant has been highlighted in the process for making wires for semiconductor devices of the next generation.
However, a wire-making process using copper and materials with low dielectric constants incurs a problem as regards the very poor etching property of copper. Accordingly, instead of conventional processes, a Damascene process (e.g., U.S. Pat. No. 5,635,423) is considered to be suitable for making copper wires.
A method of forming a copper wire for a semiconductor device according to the prior art will now be described with reference to FIGS. 1a through 1e. 
First, as shown in FIG. 1a, a first insulation film 12, an etching-interruption layer 14 and a second insulation film 16 are formed successively on a semiconductor substrate 10.
Subsequently, as shown in FIG. 1b, a first photoresist pattern 18 having a width of d1 is formed on the second insulation film 16. Then, an etching process is performed using the first photoresist pattern 18 as a mask to selectively remove the second insulation film 16 until the etching-interruption layer 14 is exposed. As a result, a second insulation film pattern 16a is formed.
Next, as shown in FIG. 1c, the first photoresist pattern 18 is removed and a second photoresist pattern 20 having a width of d2 (larger than d1) is formed on the second insulation film pattern 16a. 
Thereafter, as shown in FIG. 1d, an etching process is performed using the second photoresist pattern 20 as a mask to remove the etching-interruption layer 14 and the first insulation film 12 selectively. Through this process, i.e., a double Damascene process, a via hole 22 having a width of d1 and a trench hole 24 having a width of d2 are formed on the substrate 10.
Finally, as shown in FIG. 1e, the via hole 22 and the trench hole 24 are filled up with copper to complete a copper wire 26.
However, the method of forming a copper wire on a semiconductor device according to the prior art has a problem as follows.
A copper wire has various advantages over a conventional aluminum alloy (Al-0.5% Cu) wire. Representative examples are low electrical resistance and high reliability. However, the copper wire also has a drawback: the natural oxidation of copper. Such a natural oxidation of copper is problematic in that it decreases the reliability of the copper wire itself and even deteriorates the bonding property during packaging. Accordingly, proper measures are needed to avoid the natural oxidation of copper against long-term use of a device provided with copper wire at room temperature or a higher temperature.